/*
 *    Copyright 2009-2012 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.io;

import org.apache.commons.lang.StringUtils;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * <p>
 * ResolverUtil is used to locate classes that are available in the/a class path
 * and meet arbitrary conditions. The two most common conditions are that a
 * class implements/extends another class, or that is it annotated with a
 * specific annotation. However, through the use of the {@link Test} class it is
 * possible to search using arbitrary conditions.
 * </p>
 * <p/>
 * <p>
 * A ClassLoader is used to locate all locations (directories and jar files) in
 * the class path that contain classes within certain packages, and then to load
 * those classes and check them. By default the ClassLoader returned by
 * {@code Thread.currentThread().getContextClassLoader()} is used, but this can
 * be overridden by calling {@link #setClassLoader(ClassLoader)} prior to
 * invoking any of the {@code find()} methods.
 * </p>
 * <p/>
 * <p>
 * General searches are initiated by calling the
 * {@link #find(org.apache.ibatis.io.ResolverUtil.Test, String)} ()} method and
 * supplying a package name and a Test instance. This will cause the named
 * package <b>and all sub-packages</b> to be scanned for classes that meet the
 * test. There are also utility methods for the common use cases of scanning
 * multiple packages for extensions of particular classes, or classes annotated
 * with a specific annotation.
 * </p>
 * <p/>
 * <p>
 * The standard usage pattern for the ResolverUtil class is as follows:
 * </p>
 * <p/>
 * <p>
 * <pre>
 * ResolverUtil&lt;ActionBean&gt; resolver = new ResolverUtil&lt;ActionBean&gt;();
 * resolver.findImplementation(
 * 		ActionBean.class, pkg1, pkg2);
 * resolver.find(new CustomTest(), pkg1);
 * resolver.find(new CustomTest(), pkg2);
 * Collection&lt;ActionBean&gt; beans = resolver
 * 		.getClasses();
 * </pre>
 * @author Tim Fennell
 */
public class ResolverUtil<T> {
    /*
     * An instance of Log to use for logging in this class.
     */
    private static final Log log = LogFactory
            .getLog(ResolverUtil.class);

    /**
     * A simple interface that specifies how to test classes to determine if
     * they are to be included in the results produced by the ResolverUtil.
     */
    public static interface Test {
        /**
         * Will be called repeatedly with candidate classes. Must return True if
         * a class is to be included in the results, false otherwise.
         */
        boolean matches(Class<?> type);
    }

    /**
     * A Test that checks to see if each class is assignable to the provided
     * class. Note that this test will match the parent type itself if it is
     * presented for matching.
     */
    public static class IsA implements
            Test {
        private Class<?> parent;

        /**
         * Constructs an IsA test using the supplied Class as the parent
         * class/interface.
         */
        public IsA(Class<?> parentType) {
            this.parent = parentType;
        }

        /**
         * Returns true if type is assignable to the parent type supplied in the
         * constructor.
         */
        public boolean matches(
                Class<?> type) {
            return type != null
                    && parent
                    .isAssignableFrom(type);
        }

        @Override
        public String toString() {
            return "is assignable to "
                    + parent.getSimpleName();
        }
    }

    /**
     * A Test that checks to see if each class is annotated with a specific
     * annotation. If it is, then the test returns true, otherwise false.
     */
    public static class AnnotatedWith
            implements Test {
        private Class<? extends Annotation> annotation;

        /**
         * Constructs an AnnotatedWith test for the specified annotation type.
         */
        public AnnotatedWith(
                Class<? extends Annotation> annotation) {
            this.annotation = annotation;
        }

        /**
         * Returns true if the type is annotated with the class provided to the
         * constructor.
         */
        public boolean matches(
                Class<?> type) {
            return type != null
                    && type.isAnnotationPresent(annotation);
        }

        @Override
        public String toString() {
            return "annotated with @"
                    + annotation
                    .getSimpleName();
        }
    }

    /**
     * The set of matches being accumulated.
     */
    private Set<Class<? extends T>> matches = new HashSet<Class<? extends T>>();

    /**
     * The ClassLoader to use when looking for classes. If null then the
     * ClassLoader returned by Thread.currentThread().getContextClassLoader()
     * will be used.
     */
    private ClassLoader classloader;

    /**
     * Provides access to the classes discovered so far. If no calls have been
     * made to any of the {@code find()} methods, this set will be empty.
     * @return the set of classes that have been discovered.
     */
    public Set<Class<? extends T>> getClasses() {
        return matches;
    }

    /**
     * Returns the classloader that will be used for scanning for classes. If no
     * explicit ClassLoader has been set by the calling, the context class
     * loader will be used.
     * @return the ClassLoader that will be used to scan for classes
     */
    public ClassLoader getClassLoader() {
        return classloader == null ? Thread
                .currentThread()
                .getContextClassLoader()
                : classloader;
    }

    /**
     * Sets an explicit ClassLoader that should be used when scanning for
     * classes. If none is set then the context classloader will be used.
     * @param classloader a ClassLoader to use when scanning for classes
     */
    public void setClassLoader(
            ClassLoader classloader) {
        this.classloader = classloader;
    }

    /**
     * Attempts to discover classes that are assignable to the type provided. In
     * the case that an interface is provided this method will collect
     * implementations. In the case of a non-interface class, subclasses will be
     * collected. Accumulated classes can be accessed by calling
     * {@link #getClasses()}.
     * @param parent       the class of interface to find subclasses or implementations
     *                     of
     * @param packageNames one or more package names to scan (including subpackages) for
     *                     classes
     */
    public ResolverUtil<T> findImplementations(
            Class<?> parent,
            String... packageNames) {
        if (packageNames == null)
            return this;

        Test test = new IsA(parent);
        for (String pkg : packageNames) {
            find(test, pkg);
        }

        return this;
    }

    /**
     * Attempts to discover classes that are annotated with the annotation.
     * Accumulated classes can be accessed by calling {@link #getClasses()}.
     * @param annotation   the annotation that should be present on matching classes
     * @param packageNames one or more package names to scan (including subpackages) for
     *                     classes
     */
    public ResolverUtil<T> findAnnotated(
            Class<? extends Annotation> annotation,
            String... packageNames) {
        if (packageNames == null)
            return this;

        Test test = new AnnotatedWith(
                annotation);
        for (String pkg : packageNames) {
            find(test, pkg);
        }

        return this;
    }

    /**
     * Scans for classes starting at the package provided and descending into
     * subpackages. Each class is offered up to the Test as it is discovered,
     * and if the Test returns true the class is retained. Accumulated classes
     * can be fetched by calling {@link #getClasses()}.
     * @param test        an instance of {@link Test} that will be used to filter
     *                    classes
     * @param packageName the name of the package from which to start scanning for
     *                    classes, e.g. {@code net.sourceforge.stripes}
     */
    public ResolverUtil<T> find(
            Test test,
            String packageName) {
        String path = getPackagePath(packageName);

        try {
            List<String> children = VFS
                    .getInstance()
                    .list(path);
            for (String child : children) {
                if (child
                        .endsWith(".class"))
                    addIfMatching(test,
                            child);
            }
        } catch (IOException ioe) {
            log.error(
                    "Could not read package: "
                            + packageName,
                    ioe);
        }

        return this;
    }

    /**
     * Converts a Java package name to a path that can be looked up with a call
     * to {@link ClassLoader#getResources(String)}.
     * @param packageName The Java package name to convert to a path
     */
    protected String getPackagePath(
            String packageName) {
        return packageName == null ? null
                : packageName.replace(
                '.', '/');
    }

    /**
     * Add the class designated by the fully qualified class name provided to
     * the set of resolved classes if and only if it is approved by the Test
     * supplied.
     * @param test the test used to determine if the class matches
     * @param fqn  the fully qualified name of a class
     */
    @SuppressWarnings("unchecked")
    protected void addIfMatching(
            Test test, String fqn) {
        try {
            String externalName = fqn
                    .substring(
                            0,
                            fqn.indexOf('.'))
                    .replace('/', '.');
            ClassLoader loader = getClassLoader();
            log.debug("Checking to see if class "
                    + externalName
                    + " matches criteria ["
                    + test + "]");

            Class<?> type = loader
                    .loadClass(externalName);
            if (test.matches(type)) {
                matches.add((Class<T>) type);
            }
        } catch (Throwable t) {
            log.warn("Could not examine class '"
                    + fqn
                    + "'"
                    + " due to a "
                    + t.getClass()
                    .getName()
                    + " with message: "
                    + t.getMessage());
        }
    }

    public static String trimComma(
            String para) {
        if (StringUtils
                .isNotBlank(para)) {
            if (para.endsWith(",")) {
                return para
                        .substring(
                                0,
                                para.length() - 1);
            } else {
                return para;
            }
        } else {
            return "";
        }
    }
}